External risk intelligence

NGINX Heap Buffer Overflow Leading to Denial of Service or Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.2)

CVE-2026-15176

NGINX is a primary internet-facing web server, reverse proxy, and load balancer. It is designed to receive and process external HTTP requests directly from the internet by default, making this component public-facing in almost all standard deployment scenarios.

Buffer Overflow

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability in NGINX affects how specific configurations handle certain requests, potentially leading to a system restart or, in some cases, code execution. The primary concern is confirming whether our environment utilizes the precise configuration leading to this exposure.

Malicious requests can crash or take over the system.
High-impact risk with internet-facing servers.
Confirm exposure and assess relevance to our deployments.

Attack Path

How an attacker could exploit the issue

An attacker can exploit this vulnerability by sending specially crafted HTTP requests to a vulnerable NGINX instance. This is possible when the server is configured with specific directives like `alias` combined with `rewrite` and directives referencing the `$request_filename` variable, or when this variable is used in an access log format. The vulnerability allows for a heap buffer overflow, potentially leading to a denial-of-service or code execution under certain conditions.

No authentication required.
Crafted HTTP requests trigger overflow.
Denial-of-service or code execution.

Live Threat

Current exploitation, exposure, and threat context

An unauthenticated attacker, under specific configuration conditions for NGINX Plus and NGINX Open Source, could exploit this vulnerability through crafted HTTP requests. This may lead to a heap buffer overflow, potentially causing the NGINX worker process to restart, or in some scenarios, permit code execution when ASLR is disabled or bypassed. This issue affects the data plane only and does not expose the control plane.

NGINX worker process.
Crafted HTTP requests.
Denial-of-service or code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability affects NGINX Plus and NGINX Open Source, typically managed by infrastructure or platform teams. The first step is to identify all NGINX instances, determine their exposure and business criticality, and then assign ownership for remediation planning.

Infrastructure/Platform teams own remediation.
Verify NGINX configuration and exposure.
Plan and execute mitigation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is NGINX and why is it used?

NGINX is a widely used, high-performance web server that functions as a reverse proxy, load balancer, and HTTP cache. Because it handles incoming traffic from the internet and manages data flow to backend applications, it serves as a critical infrastructure component for delivering web content and balancing traffic across various services.

What does CWE-122 mean in the context of CVE-2026-15176?

CWE-122 refers to a heap-based buffer overflow. This is a memory corruption error where an application writes more data to a specific area of memory (the heap) than it is designed to hold. In this CVE, specially crafted HTTP requests can cause NGINX to overwrite adjacent memory, which might crash the service or potentially allow an attacker to run unauthorized code.

How do attackers trigger this heap overflow?

An attacker triggers this by sending malicious HTTP requests to a server that uses a specific, vulnerable configuration. The issue occurs only when the alias directive is paired with rewrite and variables like $request_filename, or when that variable appears in an access log format. If these specific directives are not present, the vulnerability cannot be triggered.

Do I need to worry if my NGINX instance is internal?

Halo Surface Signal indicates that because NGINX is commonly deployed to process external requests directly, it is frequently internet-facing. While external systems face the highest risk, you should evaluate any NGINX instance regardless of its network placement. Even internal systems could be reached if an attacker gains a foothold elsewhere in the network and sends the necessary crafted requests.

When should I begin my response to CVE-2026-15176?

You should prioritize identifying your NGINX footprint immediately. Start by auditing your configuration files to see if they utilize the problematic combination of alias, rewrite, and $request_filename directives. Once you map where this configuration is active, assess the criticality of those specific services to plan your remediation steps with your infrastructure or platform engineering team.

References

my.f5.com/manage/s/article/K000162416

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.